ros2 topic echo /odom covariance is unclear

Bug report

Required Info:

• Operating System: Ubuntu20.04
• Installation type: binaries
• Version or commit hash: ROS2 Foxy
• DDS implementation:
• Client library (if applicable):

Steps to reproduce issue

ros2 topic echo /odom

Expected behavior

The covariance should line up horizontally so we can see it clearer. But they’re actually arranged vertically.

Actual behavior

header:
  stamp:
    sec: 1
    nanosec: 639623972
  frame_id: /world
child_frame_id: /quadrotor
pose:
  pose:
    position:
      x: 0.0
      y: 0.0
      z: 0.0
    orientation:
      x: 0.0
      y: 0.0
      z: 0.0
      w: 1.0
  covariance:
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
twist:
  twist:
    linear:
      x: 0.0
      y: 0.0
      z: 0.0
    angular:
      x: 0.0
      y: 0.0
      z: 0.0
  covariance:
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
  - 0.0
---

Additional information

---

Feature request

Feature description

Implementation considerations

[iuhilnehc-ynos]

vertically, horizontally

Just adding the default_flow_style=True to yaml.dump could work.

or with some stride

I tried to add yaml.add_representer(list, __represent_list), but it doesn’t work. After trying to add a new Ros2Dumper derived from yaml.Dumper, and overwrite the expect_node method (unmaintainable), it seems to work as expected. Using stride = 8 as following,

child_frame_id: base_footprint
pose:
  pose:
    position:
      x: -1.987142582426784
      y: -0.4948242098096342
      z: 0.008726311344861208
    orientation:
      x: -0.00029216596084799025
      y: 0.0007255788333816825
      z: 0.3837788667705221
      w: 0.9234246962231094
  covariance: [
    1.0e-05, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0e-05,
    0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1000000000000.0, 0.0,
    0.0, 0.0, 0.0, 0.0, 0.0, 1000000000000.0, 0.0, 0.0,
    0.0, 0.0, 0.0, 0.0, 1000000000000.0, 0.0, 0.0, 0.0,
    0.0, 0.0, 0.0, 0.001]
twist:
  twist:
    linear:
      x: 6.673055220339329e-05
      y: 1.066510747665083e-05
      z: 0.0
    angular:
      x: 0.0
      y: 0.0
      z: -0.00030110521608306537
  covariance: [
    1.0e-05, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0e-05,
    0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1000000000000.0, 0.0,
    0.0, 0.0, 0.0, 0.0, 0.0, 1000000000000.0, 0.0, 0.0,
    0.0, 0.0, 0.0, 0.0, 1000000000000.0, 0.0, 0.0, 0.0,
    0.0, 0.0, 0.0, 0.001]

(Updated: make sure no more extra indent)

So I think we can provide two extra options to users,

'--show-list-pretty' 
    True : it shows [item, item2, ..., itemn]
    False : it shows
         - item
         - item2
         - ...
         - itemn
'--list-stride':
   Number: effective only if '--show-list-pretty' is True.

[RENyunfan]

Please refer to #680 (comment)

Thanks, I’d like to post the detailed steps below for anyone who has the same problem. In /opt/ros/foxy/lib/python3.8/site-packages/rosidl_runtime_py/convert.py, line 66-94, add a param in line 93 will work.

def message_to_yaml(
    msg: Any,
    *,
    truncate_length: int = None,
    no_arr: bool = False,
    no_str: bool = False
) -> str:
    """
    Convert a ROS message to a YAML string.

    :param msg: The ROS message to convert.
    :param truncate_length: Truncate values for all message fields to this length.
        This does not truncate the list of message fields.
    :param no_arr: Exclude array fields of the message.
    :param no_str: Exclude string fields of the message.
    :returns: A YAML string representation of the input ROS message.
    """
    global __yaml_representer_registered

    # Register our custom representer for YAML output
    if not __yaml_representer_registered:
        yaml.add_representer(OrderedDict, __represent_ordereddict)
        __yaml_representer_registered = True

    return yaml.dump( 
        message_to_ordereddict(
            msg, truncate_length=truncate_length, no_arr=no_arr, no_str=no_str),
        allow_unicode=True, width=sys.maxsize, default_flow_style=True,
    )